I picked this up on my Kindle when it was on sale for $.99, that was about 6 weeks ago. Since then I leveled a character of each of the 4 classes to 60, got master crafting on each, spent about $15 on runes (in game currency) during a half price rune sale and geared up a few chars to run dungeons. I only just started running dungeons, but I consider the 16 or so bucks I spent so far worth the amount of fun I had with the game.
There are separate server instances for both iOS and android so don't expect to play with friends across different OS, and each gets separate updates. The iOS version is ahead of the android one, in fact the last android update broke a bunch of quests and stuff and they still haven't gotten it fixed in about 4 weeks. Also different servers have wildly different populations, so if you enjoy a gank-filled-drama-fest experience join the more popular ones.
After the first 3 free months, there is a $1 a month subscription fee, or you can get a $3 for 6 month package which for $.50 a month is pretty reasonable to keep active just for the occasion lulz.
It is sort of a pay-to-win strategy, or at minimum a pay-to-shortcut strategy. Of course its nothing like Runes of Magic or something where I knew people spending $10,000 on a char over a 2 month period, only to have it completely outdated a month later, but you could drop a good chunck of change on a char you wanted to.
Overall a very clean professional looking game for the tablet format that lacks much of the depth of its PC big brother counterparts. All in all, I enjoyed my time spent with it, but looking forward to something a little more, hopefully in World of Midgard.